Why a heat lamp?

If we only need to have a heat lamp during the day when the emperor is hiding in his cool hide and we leave the temperature cool during the night when the emperor comes out, why do we even need to heat the aquarium? When does the emperor actually 'feel' the heat?

It needs the ambient temperature. It's essential for their metabolic rate. If they are kept for prolonged periods at low temperatures they will slowly die. The air temperature in the enclosure heats their hides to a degree. When you turn off the lamp at night, the temperature does not suddenly drop ten degrees, but rather it slowly fades. The substrate at ground level will retain some level of heat into the night and gradually cool off as well. I have two lamps on my enclosure. One gets turned off at night, and the other is on 24/7. I frequently see him "basking" under the lamp.

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Think of it as if your in a hot kitchen. You can feel the heat but your not actually by the stove. He does feel the heat in the air while in the hide assuming your providing an appropriate amount for his enclosure. If it's a hot day, your hot in the house, and even hotter outside. Then comes night time and everything gradually cools off.